We propose to study the mechanisms whereby Actinomycin D and caffeine produce modulations in the transformation frequency in vitro of cultured C3H10T 1/2 cells induced by polycyclic aromatic hydrocarbons. We will study the effects of these dose modifiers on (a) cell cycle progression, by measuring rates of DNA and RNA synthesis and by flow microfluorimetry, (b) metabolism of benzpyrene using high pressure liquid chromatography, (c) binding of benzpyrene to DNA using enzymic digestion and column chromatograhy. We will also attempt to explain the time dependency for action of these dose modifiers by studying the stability of carcinogen induced DNA lesions and the rate of production of DNA strand breaks by a sensitive new method utilizing alkaline sucrose sedimentation analysis. We finally propose to clarify the effects of cell cycle progression and further clafify factors affecting malignant trasformation by studying the cell cycle phase specificity for malignant transformation of pro- and ultimate carcinogens inducing both x-rays and UV type damage. For these studies we will develop techniques for the harvesting of mitotic 10T 1/2 cells.